In recent years, environmental regulations are becoming more and more stringent on a global scale. In particular, the circumstances surrounding automobiles, including fuel efficiency requirements and exhaust emission regulations, are becoming increasingly difficult. Behind this, there are environmental issues such as global warming, and resource protection arising from concerns about the depletion of petroleum resources. For these reasons, it is believed that further reduction of fuel consumption in automobiles will be pursued. To reduce fuel consumption in automobiles, improvement of engine oil, such as decrease of viscosity thereof, addition of a good friction modifier, etc., for the purpose of reducing friction loss in an engine, is as important as improvement of automobiles in themselves, such as weight reduction of automobiles, engine improvement, etc.
For example, PTL 1 discloses a lubricating oil composition for an internal combustion engine, which has a high-temperature high-shear viscosity at 150° C. of 2.6 mPa·s and a high-temperature high-shear viscosity at 100° C. of 5.5 to 5.9 mPa·s, thereby enabling the fuel efficiency in an internal combustion engine to be improved, and which is obtained by adding a polymethacrylate-based viscosity index improver, a salicylate-based metal detergent, a molybdenum-based friction modifier, and so on to a mineral oil-based base oil having a relatively low viscosity.